1. Field
The present disclosure relates to steerable antennas such as phase arrays. More specifically, the disclosure relates to a beamforming architecture and a method for forming beams of an array antenna that use radio frequency lens beamformers and a multi-wavelength photonic network with optical irises.
2. Description of Related Art
Phased array antenna systems are widely used in radar, electronic warfare, and radio frequency communication systems. Phased array antenna systems are characterized by the capability to steer one or more antenna beams of the antenna system by controlling the phase of the radio waves transmitted and received by each radiating element of the antenna system. Hence, a phased array antenna system does not have to be mechanically moved to provide antenna beams that move either horizontally, vertically, or in both directions.
Radio Frequency (RF) lens beamformers are known in the art and are commonly used for antenna systems. RF Lens beamformers generally comprise RF radiators positioned at the front face of the lens structure and one or more input ports positioned at the rear face of the lens structure. Typically, each input port provides RF energy to all of the radiators, but each input port is located so that the phase of the RF energy arriving at the radiators differs among the input ports. Hence, each input port provides a different antenna beam from the RF lens beamformer. RF lens beamformers known in the art include Rotman lenses, R/2R lenses, and Luneberg lenses.
U.S. Pat. No. 5,861,845, issued Jan. 19, 1999 to Lee et al., describes a wideband phased array antenna in which one embodiment uses a Rotman lens to provide a reference manifold to provide reference signal samples that are progressively time delayed. The Rotman lens may comprise an electric Rotman lens with antennas positioned on both faces of the lens or an optical Rotman lens with optical generators located on a first face and photodetectors located on a second face. The use of the Rotman lens in U.S. Pat. No. 5,861,845 highlights the capability of lens structures to provide different scanning path lengths from selected input ports to output ports.
U.S. Pat. No. 5,999,128, issued Dec. 7, 1999 to Stephens et al., describes a phased array antenna system that generates multiple independently controlled antenna beams. The phased array antenna has photonic manifolds comprising optical delay paths. Multiple antenna beams are generated by applying frequency-swept scanning signals and reference signals through the manifolds to radiative modules. Each pair of scanning and reference signals generates one of the antenna beams. The antenna beam is scanned by changing the frequency of the scanning signal. However, even though the system described in U.S. Pat. No. 5,999,128 provides multiple antenna beams, each antenna beam can generally only be coupled to a single source (i.e., transmitter) or destination (i.e., receiver). Combination of multiple beams for a single source or destination would generally require additional combinatorial circuitry.
U.S. Pat. No. 6,452,546, issued Sep. 17, 2002 to Stephens, describes phased array antenna systems that provide multiple antenna beams. Wavelength division multiplexing (WDM) networks are used to direct beam signals to selected time delay lines to provide the appropriate control over the beams. U.S. Pat. No. 6,348,890, issued Feb. 19, 2002 to Stephens, incorporated herein by reference, also describes the use of WDM networks to direct beam signals in a phased array antenna system. These patents show the desirability of optically-based antenna systems using WDM components to provide control over multiple antenna beams.
As noted above, prior art multiple beam phased antenna systems typically provide that each antenna beam may only be coupled to a single source or destination, unless additional combinatorial circuitry is used, which further complicates the architecture of such a system. Therefore, there is a need in the art for a multiple beam phased array antenna system that allows a receiver or transmitter to access multiple beams.